When determining the size of a vent pipe, which two factors are most important?

The correct answer focuses on the number of fixtures served and the length of the vent. These two factors are crucial because they directly impact the venting system's ability to function properly. The number of fixtures connected to a venting system affects the volume of air that needs to be accommodated. Each fixture will have a specific venting requirement to ensure effective drainage and to prevent the creation of negative pressure that could siphon water from traps.

The length of the vent also plays a significant role. The longer the vent pipe, the more friction losses there will be, which can reduce its effectiveness in maintaining proper air pressure and promoting the flow of wastewater. Therefore, when analyzing venting systems, it's essential to consider how many fixtures are served to determine the necessary vent diameter and how the length of the vent may affect performance.

This importance of these factors aligns with the Massachusetts Plumbing Code requirements, which guide plumbers in installing systems that ensure proper drainage and overall sanitation.